Field of the Invention
The present invention relates to a radiation detection technique and, more particularly, to a radiation detection apparatus which can obtain an X-ray image without exchanging any synchronization signal with a radiation generator, a method of controlling the same, and a non-transitory computer-readable storage medium.
Description of the Related Art
Recently, the digitization of radiation images such as X-ray images has been promoted in the medical field, leading to many merits. For example, it is possible to speed up diagnosis by allowing a user to quickly check obtained images on a display device or the like upon digital transmission to it. In addition, digitization improves diagnosis accuracy with respect to a fine lesion as well as automating diagnosis by various types of image processing. Furthermore, since there is no need to secure a film storage space, the space efficiency inside a hospital greatly improves. Moreover, since digital transmission hardly suffers deterioration in data, it is possible to transmit obtained images to a remote place without any deterioration. Making the most of these features can receive diagnosis from a highly trained doctor by transmitting images obtained in a home care site, a disaster site, or the like to a fully-equipped urban hospital.
Radiation imaging apparatuses have been commercially available and are rapidly popular, which use a digital radiography method of forming an image by converting radiation into an electric signal by using a plurality of radiation detecting elements arrayed in a two-dimensional matrix instead of a film. As a radiation imaging apparatus of this type, an X-ray detection apparatus using an FPD (Flat Panel Detector) has been proposed. In such an X-ray detection apparatus, minute X-ray detectors, each obtained by stacking a solid-state photoelectric conversion element and a scintillator which converts X-rays into visible light, are arranged, as image sensing elements, in a two-dimensional matrix, and each image sensing element converts irradiated X-rays with which an object is irradiated into an electric signal (charge amount) corresponding to the dose of irradiation. In general, an FPD can accumulate the charges, generated by X-ray irradiation, in solid-state photoelectric conversion elements by controlling a voltage to be applied to the elements. Thereafter, the FPD reads out charges from the solid-state photoelectric conversion elements by controlling the voltage to be applied to another voltage, and forms image data in accordance with the accumulated charge amounts.
When obtaining an X-ray image by using the FPD, it is necessary, in consideration of the characteristics of the solid-state photoelectric conversion elements in use, to accurately synchronize the timing of X-ray irradiation with the timing when the detectors accumulate charges (imaging). For this reason, as disclosed in, for example, Japanese Patent No 4684747, there has been proposed an X-ray imaging system which synchronizes X-ray irradiation with the timing of imaging exchanging synchronization signals between the X-ray generator and the FPD. More specifically, the FPD makes preparation for imaging in response to an irradiation request signal from the X-ray generator, and an irradiation permission signal is transmitted to the X-ray generator in accordance with the start of imaging by the FPD (the start of the accumulation of charges), thereby irradiating an object with X-rays. In the X-ray imaging system proposed in Japanese Patent Laid-Open No. 11-155847, the FPD detects the timing of X-ray irradiation by detecting a change in current caused inside upon X-ray irradiation, and starts imaging in response to the detection as a trigger, thereby establishing synchronization between X-ray irradiation and the timing of imaging.
In a system in which the X-ray generator and the X-ray detection apparatus mutually exchange no synchronization signals, the X-ray generator can generate X-rays regardless of whether the X-ray detection apparatus is ready for imaging. In this case, X-ray irradiation greatly changes the state of the X-ray detection apparatus. This influences the image to be obtained by the next imaging operation unless proper processing is performed. In order to reduce this influence, the X-ray detection apparatus may always detect the start of X-ray irradiation even before the completion of preparation for imaging as well as after the completion of preparation for imaging.
However, there are increasing cases in which since weak signals are handled for the detection or the start of X-ray irradiation, when the X-ray detection apparatus is always ready for the detection of X-rays, the apparatus erroneously detects, as imaging, an event which is not imaging because of external electromagnetic wave noise or impact. The cycle time deteriorates due to a detection error or the operation load for the restoration from a detection error increases. This leads to deterioration in the efficiency of imaging. In addition, even if noise resistance is ensured, the power consumption increases.